I suspect that the problem might be that your modules are putting out a +/-5V square wave (after looking at the MOTM/Oakley manuals). The 40106 datasheet shows that at 15V (and 25°C) the typical threshold voltages are 8.8V to switch on and 3.9V to switch off. With a +/-5V input, the 40106 is never going to switch on, so you will need some kind of voltage shifter. If you confirm that your outputs are +/-5V, I've got a very simple circuit that should make it work (hopefully).

I thought about using a proper op-amp voltage shifter, but I don't think that it's necessary. You should be able to do it with a diode and a couple of transistors as in the attached schematic.

The diode just lets through the positive parts of the square wave. The transistors are switches i.e. fully on or fully off. You need 2, as they are also inverters, so the square wave produced by the first one will be 180° with the original square wave. The second transistor re-inverts the signal. I actually breadboarded it to sanity check the circuit and it works - I've also attached the oscilloscope traces. This was at 5Hz, but it works over a wide range of frequencies.

work fine as a external module, nut not internal by breaking the signal from clock input jack.

by using as a internal modul behind the front panel, i have break the cable from ext input jack and connected this to the helper input, and connected the output to the cable that goes to the analog/digiboard input.

if i connect a clock to ext. input - sequencer works, if unplug the jack from mfos ext. in - the internal voltage is to high, with result that the internal clock don't work.

I've only just seen your post (it's 23:50) and I can see that it might cause problems as an internal (permanently connected) circuit. The easy answer would be to have it as a switchable input, which could disconnect the circuit when it's not needed. Unfortunately, this might mess up your front panel (if that's already been built).

I'll have another look at the circuit tomorrow and see if I can think of a more elegant solution. I have a couple of ideas, but I need to try them out first.

I'm not sure if I understand it correcly, but if you're using a jack with a switch contact to select between the internal clock or external, then you
could probably add a voltage divider (2 resistors or trimpot) to the internal clock before it goes to that jack._________________"My perf, it's full of holes!"http://phobos.000space.com/http://www.acidtrash.com/Stickney Synthyards

Sorry it's taken so long, but I hadn't realised quite the way that circuit works, with the external clock going through the inverter that is also the internal oscillator. I tried it out on a breadboard and nearly everything that I connected up to it caused the oscillator to stop oscillating. I thought that I'd cracked it with two "back to back" 1uF electrolytic capacitors after the 1K0 resistor on my original diagram (i.e. + to + or - to - in series). This really screws up the square wave, but the 40106 seemed to regenerate it. This appeared to be working, but I found that on some frequencies settings, the whole thing went erratic - I think that both oscillators were operating at the same time .

The only sure-fire way I can think of getting around this problem at the moment (and you're not going to like this), is by using a DPDT toggle switch to completely bypass the circuit when it's not needed. I've drawn a simple block diagram of how this would work and the connections required on a DPDT toggle switch.

If I think of a better solution, I'll let you know (or someone else might come up with it).

..,but I hadn't realised quite the way that circuit works, with the external clock going through the inverter that is also the internal oscillator.

Neither did I, I hadn't looked at the schematic , but just did and now I see what you mean. So basically the problem is that without an external
CLK connected that input needs to be left open/floating. Maybe some logic gate with a tri-state output can be used, or how about replacing the bypass
switch* in the circuit Gary drew with a digital switch (4066) that's closed when a jack is inserted. Allthough that only works with phono jacks (either
with a switch contact or using a stereo socket) not with banana's. I don't know what you are using. If you use banana's then you'll probably have to
install a switch.

For your information, I have tried a 4066 switch as PHOBoS suggested and it works perfectly. I haven't posted anything yet as I haven't drawn a diagram, but if you need any information, I can post that tomorrow.

I have been looking at switched jack sockets and it seems that normally closed switches are more common (i.e the switch opens when you insert the plug). If you have normally open switches, you just need to put one between the "voltage shifter" and XCLK, but if you have normally closed switches, you can use the circuit below, based on the 4066 bilateral switch (thanks for the tip PHOBoS). The same transistor inverter has been duplicated, so that with the jack switch closed, the 4066 is open and vice-versa. There are probably other ways of achieving this, but I have tested this and it works . You might think of uses for the other 3 switches in the 4066, but I've connected all other pins to 0V as I wasn't using them.

Nice to know that works. I think you could do it without the extra transistor, just add a pullup resistor to the CTRL pin of the 4066 (13) and use a switch
contact to GND. It also depends on the connectors you use. The ones I have don't have isolated switch contacts, so it would have to be a (NC) switch to
GND. And if you leave out R5/R6 (not bad but no need for them I think) the circuit allready get's a bit smaller _________________"My perf, it's full of holes!"http://phobos.000space.com/http://www.acidtrash.com/Stickney Synthyards

I have replaced the ext.start jack with a switch to break the output from the voltage shifter.
I cant invest to much time yet in this device, because i have to solder a yocto 808 clone until next week.
In 2-3weeks starts the TTSH, i have organized a german groupbuy for parts, so i must sort "few" parts.

Thanks for your support good guys.
I'm on muffs with same nick every day.

Nice to know that works. I think you could do it without the extra transistor, just add a pullup resistor to the CTRL pin of the 4066 (13) and use a switch contact to GND. It also depends on the connectors you use. The ones I have don't have isolated switch contacts, so it would have to be a (NC) switch to GND. And if you leave out R5/R6 (not bad but no need for them I think) the circuit allready get's a bit smaller

Yes, that sounds like it would also work (but I haven't tried it yet). I was did wonder if a simpler circuit could be used. Thanks again PHOBoS.

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